<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .list {
            width: 200px;
            height: 150px;
            background-color: skyblue;
            overflow: auto;
        }

        .news {
            height: 30px;
        }
    </style>
</head>
<body>
<!-- 1.准备好一个“容器” -->
<div id="test"></div>
<!-- 引入react核心库 -->
<script src="../js/17.0.1/react.development.js"></script>
<!-- 引入react-dom。用于支持react操作DOM -->
<script src="../js/17.0.1/react-dom.development.js"></script>
<!-- 引入babel，用于将jsx转为js -->
<script src="../js/17.0.1/babel.min.js"></script>
<script type="text/babel">
    /*
    * 生命周期的三个阶段（新）
        1. 初始化阶段: 由ReactDOM.render()触发---初次渲染
        1.constructor()
        2.getDerivedStateFromProps
        3.render()
        4.componentDidMount()
	2. 更新阶段: 由组件内部this.setSate()或父组件重新render触发
        1.getDerivedStateFromProps
        2.shouldComponentUpdate()
        3.render()
        4.getSnapshotBeforeUpdate
        5.componentDidUpdate()
	3. 卸载组件: 由ReactDOM.unmountComponentAtNode()触发
        1.componentWillUnmount()
    * */
    //定义组件
    class NewList extends React.Component {
        //初始化状态
        state = {newsArr: []};

        componentDidMount() {
            setInterval(() => {
                //获取原状态
                const {newsArr} = this.state;
                //模拟一条新闻
                const news = "新闻" + (newsArr.length + 1);
                //更新状态
                this.setState({newsArr: [news, ...newsArr]});

            }, 1000);
        }

        getSnapshotBeforeUpdate() {
            return this.refs.list.scrollHeight;
        }

        componentDidUpdate(preProps, preState, height) {
            this.refs.list.scrollTop += this.refs.list.scrollHeight - height;
        }

        render() {
            return (
                <div className="list" ref="list">
                    {
                        this.state.newsArr.map((n, index) => {
                            return <div key={index} className="news">{n}</div>;
                        })
                    }

                </div>
            );
        }
    }

    //渲染组件
    ReactDOM.render(<NewList/>, document.getElementById("test"));
</script>
</body>
</html>